1. Field of the Invention
The present invention relates to a solenoid valve which is used, for example, for controlling the injection quantity in a fuel injection system.
2. Description of the Related Art
A conventional solenoid valve 1 of this type is shown in FIG. 7. The value 1 is provided with a housing 2 in which a plug valve 4 is inserted in such a manner that it slides freely. The solenoid 16 is assembled into the housing 2 with a retainer 25 an the armature 13, which is secured on the front end of the plug valve 4 and which is housed in the armature chamber 17. The armature chamber 17 is formed between the housing 2 and the solenoid 16 so as to face oppose the intake end surface 37 of the solenoid 16. The structure of the solenoid 16 is known in the art. The solenoid 16 includes coils 22, housed within coil grooves 21a of a stator 21 and a core plate 23 which is connected with the stator 21 with a surface thereof aligned with the intake end surface 37. At the same time, a resin mold 24, formed from a synthetic resin, covers the portions of the stator 21 and the coils 22 that protrude to the outside from the core plate 23. Also, resin fills the opening area of the coil grooves 21a within a range so that it does not protrude from the intake end surface.
At the side portion of the plug valve 4, towards the front in the figure., a fluid passage 34 is formed, which communicates with the compression space of the injection pump, and communication between the fluid passage 34 and the armature chamber 17 is adjusted by the valve mechanism that is formed by the housing 2 and the plug valve 4. Also, the armature chamber 17 is connected with the fuel supply side via a fluid passage (not shown) and a force is applied to the plug valve 4 by a spring 9 in a direction that constantly separates the armature from the solenoid 16.
However, the fuel that charges into the armature chamber 17 via the fluid passage 34 is under extremely high pressure; for example, approximately 1500 kg/cm.sup.2 during the compression phase of the injector unit, and since, in the solenoid valve 1 described above, the stator 21 of the solenoid 16 is held by the resin mold 24, when the high-pressure fuel passes around the armature and presses down on the intake end surface 37 of the solenoid 16, the resin mold 24 becomes deformed. Then, as shown in FIG. 8, both sides of the stator 21 are deformed so that they go toward the center, as indicated by the arrows, to distort the intake end surface 37 of the stator 21. Note that in FIG. 8 the distortion is greatly exaggerated to facilitate explanation.
The gap between the stator 21 and the armature 13 is extremely small; approximately 0.1-0.2 mm, and there is a problem in that if the stator 21 becomes distorted as shown in FIG. 8, every time high-pressure fuel is charged, the gap between the stator 21 and the armature 13 changes, making the performance of the solenoid valve unstable.
Also, there are problems such as the fact that the surface of the solenoid undergoes plastic deformation over time because of the charge of high-pressure fuel and the high-pressure fuel entering between the stator 21 and the resin mold 24 due to the deformation of the stator 21 to rupture the resin mold 24 as shown in FIG. 8.
One solution to the problems described above is disclosed in Japanese Patent Unexamined Publication H4-82361. Here, a thin, non-magnetic metal plate is provided on the intake end surface of the solenoid. However, as mentioned above, the gap between the stator and the armature is extremely small and the distance between the stator and the armature will increase by an amount equivalent to the thin plate and this results in reduced performance and responsiveness.